Full text of "Silvical Characteristics of the Loblolly Pine"

Station Paper No. 98

December 1958

Silvical Characteristics of Loblolly Pine

Karl F. Wenger

SOUTHEASTERN FOREST
EXPERIMENT STATION
Asheville, North Carolina

flodeph 3. Peckanec,
Jul rector

U. S. DEPARTMENT OF AGRICULTURE - FOREST SERVICE

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Silvical Characteristics of Loblolly Pine

(Pinus taeda L. )

Karl F. Wenger
Southeastern Forest Experiment Station

Because of its wide range, its occurrence in pure stands, its abundance,
and its versatility in use, loblolly pine ( Pinus taeda ) is the principal commer-
cial species in the southeastern United States (fig. 1). It grows in the Coastal
Plain and Piedmont from central Maryland and Delaware south to central
Florida and west to eastern Texas (fig. 2) (72). It does not grow in the Mis-
sissippi River bottoms and is scarce in the deep, coarse sands of the lower
Gulf Coastal Plain and sandhills of North and South Carolina.

HABITAT CONDITIONS

CLIMATIC

The climate of the loblolly pine range is humid, with long, hot summers
and mild winters. Average annual rainfall varies from 40 to 60 inches per year;
it is least in Maryland and Delaware and at the western end of the range in east
Texas ( 124) . Along the Gulf Coast it averages 60 inches. Summer is usually
the wettest season and autumn the driest along the mid- Atlantic Coast. In the
western portion of the range, rainfall is more uniformly distributed through
the year, but summer droughts occur often enough to be a serious obstacle to
natural regeneration and planting of the species.

The frost-free period lasts from 6 months in the North to 10 months in
the South. July temperatures average over 75° F. and frequently exceed 100°;
January temperatures average 36° to 63° and occasionally go down to -10° in
the northern and western portions of the range.

The distribution of loblolly pine is associated with the average winter
temperature, and the frequency and intensity of both winter and summer rain-
fall (57). During both winter and summer, the area within the range of loblolly
pine has a greater number of days with rain and a greater frequency of effec-
tive amounts of rain (more than 0.50 inch) than the area immediately outside
the range. The area inside also has a higher average temperature in winter.
In spring and autumn, the weather inside and outside the range is more nearly
the same. The main factor limiting northern extension of the species is prob-
ably temperature, but the western extension is probably limited by precipitation.
Low air temperatures damage aerial portions, and low soil temperatures retard
water absorption more in loblolly pine than in native northern species (65).
Damage by snow and sleet, which is less frequent within the range, may also
be a factor limiting the northern extension.

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Figure 1. --Mature loblolly pine tree in the Crossett Experimental Forest, Crossett, Arkansas.

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EDAPHIC

Loblolly pine occurs on a wide variety of soils, from the flat, poorly
drained, ground-water podzols of the lower Coastal Plain to the old residual
soils of the upper Piedmont. It grows best in soils with poor surface drain-
age, a deep surface layer, and a firm subsoil (48, 150 ).

Such soils are common in the lower Coastal Plain and in the flood
plains of the larger rivers. Prominent examples are the Coxville and Bladen
series; with deep surface layers these soils have a site index for loblolly of
90 to 95 feet (48). In the same category is the Elkton series: poorly drained,
very plastic soils which have an average site index of 95 feet. Most produc-
tive are the river bottom or terrace soils, notably the Roanoke series in the
east and the Ocklockonee in the west; these are fairly heavy soils that have
site indices of over 100 feet (2A, _48). In the Coastal Plain, the productivity
of soils decreases with improvement in surface drainage. The presence of a
hardpan within the root profile, as in the Leon series, drastically reduces
the productivity. Deep, excessively drained sands are also very low in site
quality ( 24 ) unless the water table lies within reach of the tree roots; with
high water tables sands may have site indices of 90 to 100 feet.

In the inland and Piedmont regions, where surface drainage is well-
developed, the physical characteristics of the soil, rather than drainage,
determine the availability of moisture, and uneroded soils with a deep sur-
face layer and a friable subsoil are best (J36). Common in this category are
soils of the Durham, Georgeville, Appling, Cecil, Davidson, and Lloyd
series, which have site indices of 80 to 100 feet when not eroded. The least
productive are eroded soils with a very plastic subsoil. Iredell, Orange,
and Whitestore (red phase) series fall in this group; they are practically
worthless when the A horizon is gone, with site indices of less than 40 feet.

PHYSIOGRAPHIC

The range of loblolly pine extends over two main physiographic regions,
the Coastal Plain and the Piedmont. The Coastal Plain is generally very flat
near the coast but becomes rolling and even sharply hilly in the inland reaches
with elevations ranging up to 1,000 feet in Georgia. Topography in the Pied-
mont is more rolling than in the Coastal Plain, with highly developed drainage
patterns and generally heavier soils. Elevations range up to 1,500 feet. In
northern Alabama and Georgia, loblolly pine grows at elevations up to and
over 2,000 feet.

The rougher topography of the Piedmont results in greater variations
in site than in the Coastal Plain. Loblolly pine site indices generally in-
crease from ridge tops to bottoms but this variation seems to be related to
soil differences rather than to slope position or steepness (35). Soil fea-
tures that determine site quality, such as surface soil thickness and sub-
soil consistency, are loosely correlated with topography, but past land use,
differences in soil parent material, and other factors also affect soil profile
development and cause variations in site quality independent of topography.

- 4

Because of plentiful rainfall, rolling topography, and soil physical char-
acteristics, the upland soils of the Piedmont and many sections of the upper
Coastal Plain are subject to moderate to severe sheet and gully erosion
when exposed and unprotected. The loss of surface layers in the past has un-
doubtedly contributed to the prevailing poor site quality of upland soils in the
region (39).

BIOTIC

Pure loblolly pine stands are widespread throughout the range where
moisture is comparatively plentiful (fig. 3). In general, the main associate
is sweetgum ( Liquidambar styraciflua), but on well-drained sites shortleaf
pine ( Pinus echinata ), southern red oak ( Quercus falcata ), post oak (Quercus
stellata ), and blackjack oak ( Quercus marilandica ) are frequently found with
it. On poorly drained sites black tupelo ( Nyssa sylvatica ), water oak (Quercus
nigra) , yellow-poplar ( Liriodendron tulipifera ), and pond pine ( Pinus serotina),
and in the far south slash pine ( Pinus elliottii ) and laurel oak (Quercus
laurifolia ), usually occur in loblolly pine stands ( 113 ).

In east Texas, southern Arkansas, Louisiana, and to a lesser extent in
other states, mixtures of loblolly pine and shortleaf pine occur, with short-
leaf pine predominating on the drier ridges and loblolly pine on the wetter
sites. Commonly associated with these species are sweetgum, black tupelo,
hickories ( Carya spp. ), southern red oak, scarlet oak ( Quercus coccinea ),
black oak ( Quercus velutina) , white oak ( Quercus alba) , post oak, and minor
species.

Loblolly pine also grows in mixtures with hardwoods throughout its
range. On wet sites sweetbay ( Magnolia virginiana) , redbay (Persea borbonia),
black tupelo, swamp tupelo ( Nyssa sylvatica var. biflora ), and sweetgum are
prominent in the hardwood component; water oak, laurel oak, willow oak
( Quercus phellos ),red maple ( Acer rubrum) , white ash ( Fraxinus americana ),
green ash ( Fraxinus pennsylvanica ), and American elm (Ulmus americana )
are frequently present. On drier sites southern red oak, white oak, northern
red oak ( Quercus rubra ), hickories, common persimmon (Diospyros virginiana ),
and scarlet oak are the most common hardwoods, and shortleaf and longleaf
pine ( Pinus palustris ) are frequent associates.

In the Piedmont, and in the Coastal Plain of northern Virginia and
Maryland, loblolly pine also occurs with Virginia pine ( Pinus virginiana ). In
northern Mississippi, Alabama, and in Tennessee it is a minor associate in
the eastern redcedar-hardwood type. On moist sites, loblolly is found in the
longleaf pine type, the longleaf pine- slash pine type, and in the slash pine-
hardwood type. In the flood plains of major rivers it is a minor associate in
the swamp chestnut oak- cherrybark oak type. On moist lower slopes in the
Atlantic Coastal Plain it is an important element in the sweetgum-yellow-
poplar type. In bays, ponds, swamps, and marshes of the Coastal Plain it
is a common associate in the pond pine type, the cabbage palmetto- slash
pine type, and in the sweetbay- swamp tupelo- red maple type ( 1 13 ).

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Because of the wide range of sites and the numerous types in which lob-
lolly occurs, a great variety of lesser vegetation may be found in association
with it and a list of even the most common would be quite lengthy. Worthy of
mention are waxmyrtle ( Myrica cerifera ), pepperbush ( Clethra alnifolia ),
gallberry (Ilex glabra) , viburnums ( Viburnum spp.), and a great variety of
ericaceous shrubs.

In the natural state, mycorrhizae usually occur on loblolly pine. In-
fection by several species of fungi causes proliferation of the short roots,
characterized by repeated dichotomous branching. This proliferation and the
accompanying mantles of fungal hyphae greatly increase the absorbing surface,
and conifers in infertile soil without mycorrhizae are very low in mineral
content compared to those with mycorrhizae. Mycorrhizae apparently can also
supply carbohydrates from the soil, although they seem primarily dependent on
those in the plant ( 148 ). They also supply nitrogen compounds, and may be
able to supply vitamins. Among the fungi capable of producing mycorrhizae
in loblolly pine, the following have been identified (42, 55): Boletus granulatus ,
Boletus exinus, Boletus brevipes , Boletus chromapes , Boletus subluteus ,
Boletinus pictus, Cantharellus cibarius, Cenococcum graniforme , Russula
lepida , and Amanita muscaria .

Few of the animals that live within the range of loblolly pine are associ-
ated with it by a closer tie than the accident of location. Probably the most
noteworthy is the red-cockaded woodpecker ( Dryobates borealis) (115). This
bird invariably digs its nesting cavity in a living pine tree with red heart
( Fomes pini) . When the cavity is finished, the bird pecks the bark all around
the entrance hole, causing a heavy flow of pitch. The surface around the
entrance hole thus becomes very sticky, presumably keeping out intruders.
Among other birds frequently found in pine forests in the South are the brown-
headed nuthatch ( Sitta pusilla ), the pine-woods sparrow (Peucaea aestiyales
aestivales ), the southern pine finch ( Peucaea aestivales bachmani ), the pine
warbler ( Dendroica vigorsi ), and the prairie warbler ( Dendroica discolor) (1 15).

Four-footed animals are scarce in full stands, but after clear cutting,
rodent populations increase rapidly. White-footed mice and red mice
( Peromyscus spp.), harvest mice ( Reithrodontomys humulis ), pine mice
( Microtus pennsylvanicus ), cottonrats ( Sigmodon hispidus ), and short-tailed
shrews ( Blarina brevicauda) are common in cutover areas in eastern North
Carolina ( 121 ). Gray squirrels ( Sciurus caroliniensis ) are fond of pine seed
and begin to shell out cones in late summer, as soon as the seeds are well
filled.

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LIFE HISTORY OF THE SPECIES

SEEDING HABITS

Flowering and fruiting . --The development of loblolly pine seed requires
nearly three growing seasons from the time of flower bud initiation. Flower
buds are formed during midsummer, some time after the middle of June, but
do not become visible until early autumn. Staminate flower buds can be seen
in the South Atlantic Coastal Plain during October as small knobs around the
base of vegetative buds. Later, some vegetative buds develop pointed swell-
ings near the apex, which are pistillate flower buds. These flower buds grow
rapidly in late winter and for a short time before flowering the staminate buds
are very prominent.

Vegetative growth begins about March 1 in the Gulf States and about 6
weeks later near the North Carolina-Virginia boundary (44). Flowers mature
and pollen cast begins about 10 days later ( 131 ). The staminate flowers are
long, yellow catkins, and the pistillate flowers are small, pink or red strobili.
Pollination lasts 7 to 10 days. Staminate flowers usually are the most plentiful
and are borne all over the crown, while pistillate flowers tend to be concen-
trated in the upper portions of the crown. On the same tree, staminate flowers
tend to mature before pistillate flowers ( 128 ). Thus, pollination depends largely
on pollen from neighboring trees and may be inhibited if trees shed pollen at
different times or are too far apart. In general, pine pollen is not carried
in effective quantities farther than 300 feet, and most falls much closer to the
source ( 146 ).

Within the pistillate strobili the growing pollen tubes do not reach the em-
bryo sac to fertilize the egg cells until late the following spring. By that time,
the strobili have become conelets one-half to three-fourths of an inch long.
Growth of cones and seed is rapid during the second season, after fertilization
occurs.

Cones mature and seed ripens usually during the early part of October.
Time of seed ripening does not appear to vary greatly with latitude (44).
Individual cones may contain from less than 20 to more than 200 seeds, sound
and defective ( 131 ).—/ The percentage sound may vary from about 15 percent
up to nearly 100 percent. In southeastern Virginia, the average number of
sound seeds per cone varied from 30 in stands averaging only 1 cone per tree
up to 110 in stands averaging 150 cones per tree.— The over- all average
was 57 sound seeds per cone.

The seeds vary in size from 16,000 to 25,000 per pound and average
18,400 per pound (126).

1/ Records of the Tidewater Forest Research Center, Franklin, Virginia,
1952.

2/ Wenger, K. F. Seed tree stimulation study. 1951. (Report on file,
Southeast. Forest Expt. Sta.)

8 -

Seed production . --Individual loblolly pine trees occasionally produce
cones and viable seed at less than 10 years of age. Pistillate flowers have
been observed on 5-year-old trees, staminate flowers on 6-year-old trees
( 106 ), and viable seed have been obtained from 9-year-old trees (132). But
appreciable quantities of seed are not produced until much later. Seed pro-
duction of dominant and codominant trees in undisturbed, even-aged stands
increases gradually until the trees are 30 to 50 years old and 12 inches or
more in diameter (99). It then increases rapidly until the full potential is
attained. However, the viability of seed from young trees just beginning to
bear is as high as that of seed from older trees ( 131 ).

Although loblolly pine stands are capable of heavy seed production to
advanced ages, seed crops fluctuate widely from negligible amounts in some
years to nearly a million seeds per acre in other years. Seed crops of a
70-year-old stand in North Carolina Piedmont varied from 18,000 to nearly
300,000 seed per acre during 13 years from 1936 to 1948 ( 101 ). Seed pro-
duction tends to be better in the coastal portions than in the inland portions
of the loblolly pine range ( 128) , and annual seed crops of one 95-year-old
and two 145-year-old stands in northeastern North Carolina ranged from
50,000 to 832,000 seed per acre from 1947 to 1954. A partially cut 35- to
45-year-old stand in coastal South Carolina produced 1.4 million seeds per
acre in 1955, which is apparently the greatest seedfall recorded in loblolly
pine up to that year (77).

The annual fluctuations in seed crops depend mainly on weather and
the physiological status of the trees at the time of flower bud formation. In
the three stands in northeastern North Carolina, the size of seed crop was
positively correlated with the May- to- July rainfall of 2 years earlier and
negatively correlated with the size of the seed crop 2 years earlier ( 142 ).

Although conditions may favor a heavy set of flower buds, many agen-
cies may reduce or destroy the cone crop before maturity. Flowers may be
destroyed by subfreezing temperatures, heavy rain, hail, or strong winds,
or rainy weather may inhibit or prevent pollination. Drought may retard
development, and insects damage both cones and seed.

Cone damage varies from year to year, usually amounting to 10 to 40
percent but may often be more or less in any given locality (63). Cone losses
on individual seed trees in southeastern Virginia, caused mainly by insects,
varied from 2 to 100 percent in one year and from 4 to 71 percent in the follow-
ing year. Losses were greater in small crops than in large crops, and trees
that sustained heavy losses in one year also had heavy losses in the next year.
Most of the insect damage probably is caused by the larvae of a small moth,
Dioryctria amatella (63), but cone beetles, mainly Conophthorus taedae, may
also cause appreciable losses (40). Another small moth, Laspeyresia toreuta ,
destroys a small proportion of the individual seeds without otherwise damag-
ing the cones (63). Insect damage tends to be higher in older stands and on
better sites.

9 -

The quality of seed also varies from year to year with the size of the
seed crop. In both the Piedmont and Coastal Plain of North Carolina via-
bility ranged, on the average, from a little more than 40 percent in light
crops to nearly 80 percent in heavy crops ( 101 , 143 ). In individual stands,
viability as low as 25 percent occurred.

Individual dominant and codominant trees in undisturbed stands may
bear as many as 500 cones but most trees bear less than 100 cones. Inter-
mediate and suppressed trees may never produce good crops. Fruitfulness
apparently is hereditary to some degree, and cone crops of individual trees
are closely related to past fruitfulness ( 45 , 52, 99, 137). Cone crops are
also proportional to diameter at breast height, and crown volume and crown
density have been found to affect size of cone crops (53).

In the Atlantic Coastal States, cone and seed production of individual
dominant and codominant trees released from competition and of stands par-
tially cut increased 2- to 10-fold three growing seasons later (46, 99 , 1 19 , 137 )
Trees of larger diameter and greater past fruitfulness produced much larger
crops after release than smaller or less fruitful trees. As many as 1,500
cones may develop on some trees after release but most trees bear less than
500 cones. The response to release is greater when it coincides with good
seed years; in partially cut stands it seems to be proportional to the intensity
of cutting. It usually persists for several succeeding crops but eventually
subsides (46, 137 ).

The cone crop in the third succeeding fall is larger if the release cut-
ting is done before late spring. In the South Atlantic Coastal Plain the crit-
ical period is some time during late June or July- -release during or after
that period is not reflected in cone crop until the fourth succeeding year.
The reduction in transpiration accompanying the removal of competing trees,
which is probably equal to several inches of rain, may be the primary cause
of the increase in cone crops following release (142).

Seed dissemination . --Seedfall usually begins during the early part of
October and does not vary greatly with latitude (44). It reaches a peak very
quickly and then declines. By January 1, 80 to 90 percent of the seed has
fallen, although some continues to fall until late spring. Seedfall is hastened
by dry, warm, windy weather and retarded by cool, wet weather (59) . Via-
bility of the seed is highest at the peak of the seedfall. Seed falling later is
progressively lower in viability until the end of seedfall in the spring.

Although loblolly pine seed is entirely wind-disseminated, and was
apparently carried 2.5 miles from the source in one case ( 104 ), it is usually
not dispersed in effective quantities more than 300 feet. In strip cuttings in
North Carolina, 67 percent of the seed fell within 100 feet and 85 percent
fell within 200 feet of the windward uncut strip ( 101 ). In old fields, where
seed dispersal was less restricted, the number of seedlings established fell
below 1,000 per acre at 330 feet from the seed source, and beyond 462 feet
was less than 500 per acre (83).

VEGETATIVE PROPAGATION

When 1- to 3-year-old seedlings of loblolly pine are decapitated or in-
jured, they sprout readily from buds formed in the axils of primary needles
( _1_16, 1_17) . J/ Older seedlings and trees do not sprout. Rooting ability is 1/

similarly confined to young seedlings. Nearly half of the cuttings from
1-year-old seedlings rooted, but only 6 percent rooted from 2-year-old
seedlings, and none rooted from 3-year-old seedlings (49). Rooting by air-
layering has been somewhat more successful. Six of ten 2|-year-old seed-
lings developed roots in air- layers in one test ( 152 ), and good results were
obtained with 3- and 5-year-old seedlings in another (20). In the latter test,
results were poorer with older trees but air- layers even from 60-year-old
trees developed a few roots.

Loblolly pine has been successfully grafted by several methods. In
very limited tests, one-half or more soft-tissue grafts were successful (_1_5_1).
These included loblolly scions on loblolly and shortleaf stocks and shortleaf
and slash scions on loblolly stocks. Side grafts of loblolly on loblolly were
completely successful when made in April and somewhat less successful when
made in February and March (31). Wedge grafts were least successful.

SEEDLING DEVELOPMENT

Establishment . - - Birds and rodents probably eat appreciable amounts of
seed between seedfall and germination, but apparently not enough to hinder
natural regeneration ( 143) except in poor seed years. Bob- white quail (Colinus
virginianus ) in eastern Maryland have been found to eat pine seed in preference
to wild and cultivated leguminous seed ( 145 ). However, as many as 89 percent
of sound seeds may fail to germinate ( 100 , 126 ). Further losses occur because
of limited moisture related to seedbed conditions and the failure of the radicle
of germinating seeds to penetrate hard soil surfaces and deep litter ( 51 , 100 ).

Moisture remains the most important factor in survival throughout the
first growing season. The greatest mortality occurs shortly after germination
( 47 ) and tends to be higher in lighter soils. Droughts after midsummer, when
soil moisture is already quite low, may also cause heavy mortality, particularly
where competing vegetation is abundant. A study in Arkansas showed that most
new seedlings established on third-year and older seedbeds had disappeared by
the following year (86), probably because of competition from hardwood brush.

Losses from these various causes are reflected in the large number of
sound seeds needed to establish a seedling, even on the best seedbed. In
northeastern North Carolina, the number of sound seeds needed to establish
1 seedling on fresh seedbeds averaged 9 on exposed mineral soil, 15 on burned
soil surfaces, and 40 on undisturbed litter and logging slash ( 1 18 ). A similar
effect of seedbed condition on seedling establishment was observed in south-
eastern Arkansas (51). Thus, much larger amounts of seed are required for

3/ Little, S. Official correspondence, Southeast. Forest Expt. Sta.
1957.

- 11 -

satisfactory reproduction on undisturbed litter than on mineral soil. Favor-
able seedbed conditions disappear rapidly, and about four times as many
seeds are needed on second-year as on first-year seedbeds to establish one
seedling 0J6, 120 , 141 ). By the third year, initially favorable seedbeds have
become nearly as unfavorable as undisturbed litter.

Natural regeneration of loblolly pine thus depends on adequate amounts
of seed in the first year after logging or seedbed preparation ( 120 ). In small
ownerships adequate seed can often be obtained by postponing harvest cutting
until after seedfall. The seed-tree method gives the greatest control of the
seed supply through variations in the numbers of seed trees ( 140 ), but adequate
seed can also be obtained from seed strips. Seed is usually more plentiful in
stands managed by the selection method because of the large number of seed-
bearing trees and the stimulation of seed production by repeated cutting.

Where the bulk of a well- stocked stand is cut, tractor logging exposes
mineral soil on about 50 percent of the logged area, which is usually suffi-
cient for satisfactory regeneration in good seed years ( 1 18 ). In mediocre
seed years, however, or with less effective logging methods, additional site
preparation is essential. Scarification with a bush-and-bog diskharrow or
burning before or after logging have been successful ( 23 , 30 , 73 ) and will
usually compensate for the lower seed supply in mediocre seed years.
Periodic winter fires throughout the rotation, with the last fire just before
the harvest, or several annual summer fires before the harvest, have also
been tested with considerable success (7J3, 105 ). The effects of site prepa-
ration on the amount of hardwood brush persist for several years, so that a
greater percentage of established seedlings become dominant ( 75 , 143 ) .

In poor seed years, the number of seed trees needed becomes prohib-
itively large, even with intensive seedbed preparation, unless the seed trees
are selected and released from competition 3 to 5 years before the harvest
cut. In the South Atlantic Coastal Plain, released trees produce enough seed
for adequate regeneration even in poor seed years ( 140 ). Since heavy cone
crops are evident a year before maturity ( 1 19 ) and are usually followed by a
poor crop 2 years later, poor seed years apparently can be predicted far
enough in advance so that trees can be released in time to supply increased
amounts of seed in the poor year ( 142 ).

Early growth. --The resumption of growth in the spring is mainly a
response to rising air temperature but is also influenced by soil temperature
(64). -3/ It usually occurs before the date of the last killing frost (66), in late
March or early April in the northerly portions and about a month earlier in
the southerly portions of the range. Twenty percent or more of the year's
height growth occurs each month from April to August and is usually at least
80 percent complete by July 1 in all parts of the range (66^ 103, 144 ). Vigorous
seedlings make several surges of height growth, normally three, during a
growing season; the first is the longest and the last is usually very short (138).

4/ Hahn, V. W. The effect of soil and air temperatures on the resump-
tion of growth of tree seedlings in the spring. 1942. (Unpublished Master's
thesis, Duke University, Department of Botany.)

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Best growth occurs when night temperatures are 12 to 13 C. lower than day
temperatures (JO). Thus, slowing of height growth in midsummer may be due
in part to high night temperatures. High night temperatures may also be an
important factor in the generally slower growth of loblolly pine along the Gulf
Coast. Height growth ends in late summer, before air temperatures become
unfavorable and apparently in response to shorter periods of daylight (64).
Foliage is usually retained till the end of the second growing season,although
it may be cast earlier if infected by the needle-blight fungi, chiefly Lophoder -
mium pinastri and Hypoderma lethale (9^, 11).

Roots of loblolly pine grow at all times of the year ( 103 , 123 ). Most
root growth occurs in spring (April and May), and in late summer and early
fall; least root growth occurs in winter and midsummer. Growth in winter
is limited by low temperatures, none having been observed at less than 53° F.
( 123 ). Growth in summer is limited by low soil moisture and high tempera-
tures. Optimum temperature is 77° F. and root growth ceases between 86°
and 95° (103).

During the first 5 to 10 years, height growth of vigorous loblolly pine
seedlings follows a rising trend, and may average 2.5 feet per year ( 12 , 127,
138 ). Under favorable conditions, seedlings may reach 2 feet in height in the
first year but the average first-year height is about 4 inches ( 102 ). In North
Carolina, first-year seedling heights varied with soil surface conditions; the
tallest 10 percent of seedlings present exceeded 11 inches in severely burned
areas, 7 inches on bare soil or disturbed litter, and 5 inches in undisturbed
litter, slash piles, and lightly burned spots. The better growth in severely
burned areas was still evident at 5 years ( 138 ). Light shade apparently is
beneficial in the first year (8); thereafter it is not.

In the Coastal Plain of North Carolina, seedlings grew faster in sandy
loams with friable subsoils than in silt loams with plastic subsoils ( 139 ).
Seedlings on the better soils also had larger crowns. In a study of potted
seedlings, growth was least in sand and best in a silty clay ( 136 ). Loosening
of the soil by disking apparently aids height growth during the early years ( 139 ),

Height growth of loblolly pine seedlings is inversely related to the stock-
ing of larger trees within a 30- foot radius and directly related to level of
shade ( 12_, J29 ) . In Arkansas, heights of 5-year-old seedlings ranged from
0.8 foot under a full canopy to 10.0 feet in large openings ( 127 ). -^ In 8- to
15-foot openings, seedlings were 2.6 feet tall in 5 years; this rate of growth
was judged to be adequate for survival, but in smaller openings growth was
less. In Georgia, the average seedling was 0.7 foot shorter for every 10-foot
lower shade level (12). If the over-topping trees are hardwoods, seedling
growth is still less- -in Arkansas seedlings were 0.14 foot shorter for every
10 percent increase in the basal area of hardwood cover. -^ Seedlings growing
beneath larger hardwood trees invariably die if they are not released. In a

5/ Wahlenberg, W. G. Effect of overwood on survival and development
of loblolly pine seedlings in southern Arkansas. 1946. (South. Forest Expt.
Sta. office report.)

study in Louisiana, no seedling established under hardwood shade survived
for more than 19 years, and the average period of survival was 5.27 years
(29). Seedlings that grow less than 6 inches annually in height probably will
not survive ^29, 127, 138 ).

Low- level competition from hardwood shrubs and sprouts reduces
height growth and is often fatal to loblolly pine seedlings. Approximately 80
percent of overtopped 3-year-old and older seedlings and 15 to 40 percent of
seedlings with side competition do not survive ( 109 , 138 ). Height growth and
crown expansion of hardwood sprouts is rapid during the first 3 years and
much slower thereafter (1_3_, 138) . Consequently, seedlings that are not over-
topped at 3 years or later have a good chance of outgrowing the competing
hardwoods.

These variations in seedling growth are responses mainly to differences
in light and soil moisture caused by competing hardwoods. The maximum rate
of photosynthesis is greater in hardwoods than in loblolly pine, and the hard-
woods reach their maximum rate at one- third or less of full sunlight (61, 68).
Pine reaches its maximum rate at that light intensity only in the first year,
because the primary needles are so arranged that they shade each other very
little (8). But the arrangement of secondary needles on older seedlings results
in much mutual shading ( 67 ) and photosynthesis proceeds in proportion to light
intensity, reaching the maximum rate only in full sunlight (61, 68). Low light
intensity also reduces photosynthesis through its effect on water absorption.
Pine root systems are smaller than hardwood root systems under full light
but the difference becomes much greater under partial light (34, 61, 62, 136 ).
Thus, absorption is retarded under partial light, even when soil moisture is
ample, and moisture stress in the seedlings is increased, which reduces the
photosynthetic rate. When soil moisture is also low, the moisture stress in
the seedlings is still greater. Thus, photosynthesis is reduced more rapidly
in pine than in hardwoods by decreasing soil moisture C7, 59).

Since low light intensity and low soil moisture usually occur together
under natural conditions, loblolly pine suffers much more than the hardwoods
from competition. In the first year, moisture is evidently the more important
factor; in a study in North Carolina, pine seedlings in their first year did not
respond to increased light at low moisture levels (47). After the first year,
light is the more important factor; loblolly pine seedlings in the shade do not
develop root systems large enough to supply the moisture needed for survival.
With ample light, root systems are larger and supply the water and nutrients
needed for survival even with soil moisture as low as that within a stand ( 69 ,
95). However, either deficient light or deficient soil moisture will retard
growth; if both are deficient the seedlings usually die (60).

Too much water may also be detrimental to seedling growth and sur-
vival, although loblolly pine can endure prolonged flooding of the roots better
than pond pine, its wet- land associate. One test of various periods of flood-
ing showed that at least 10 months of continuous flooding with standing water
was needed to permanently injure roots of loblolly pine seedlings (58). Pond
pine showed permanent injury by failure to make normal height growth during

- 14 -

periodic drying after 3 months of continuous flooding. Another test showed
that loblolly pine could endure flooding for a 50-percent longer period than
pond pine.-"-/

Growth and survival of loblolly pine seedlings are also affected by in-
sect and disease attacks. Repeated attacks by the Nantucket pine tip moth
( Rhyacionia frustrana ) reduce height growth and cause crooking and forking
but usually do not cause mortality. The pales weevil ( Hylobius pales ) and its
close relatives may kill planted seedlings in large numbers in recently cut or
burned areas but have not been important in natural reproduction. The red-
headed pine sawfly ( Neodiprion lecontei ) and the pine webworm ( Tetralopha
robustella) can cause mortality by defoliation and occasionally cause large
losses in limited localities. In many localities west of the Mississippi the
Texas leaf- cutting ant ( Atta texana ) is a serious pest on natural and planted
seedlings, and control measures are necessary.

The most common disease is fusiform rust ( Cronartium fusiforme).
It causes lethal stem and branch cankers and has oak as an alternate host.
The brown spot needle disease ( Scirrhia acicola ) is common in some areas
and heavy infections probably check growth ( 10).

SAPLING STAGE TO MATURITY

Growth and yield . --Pure, even-aged stands of loblolly pine vary greatly
in growth and yield in response to differences in site quality. Individual trees
in particularly favorable locations may attain diameters of 50 to 60 inches and
heights of 150 feet at advanced ages (2). The largest recorded loblolly pine
presently in existence is located in Dinwiddie County, Virginia, and is 63 inches
d.b.h. and 128 feet tall (1); another in Hertford County, North Carolina, is 54
inches d.b.h. and 151 feet tall. The average tree is much smaller. Sizes
attained by average trees in the dominant portion of well- stocked, unmanaged
natural stands are shown in the tabulation below ( 125). Trees in managed stands

would be

considerably

larger in

d.b.h. at the same

ages.

Site Index

60 feet

Site Index

90 feet

Site Index

120 feet

Age
(Years)

D.b.h.
(Inches)

Height
(Feet)

D.b.h.
(Inches)

Height
(Feet)

D.b.h.
(Inches)

Height
(Feet)

4.6

6.9

8.5

6.6

9.6

11.9

8. 1

11.7

14.6

108

9.4

13.6

16.8

120

10.4

15.0

18.6

128

6/ Gaiser, R. N. The growth of loblolly and pond pine seedlings under
differing conditions of soil flooding. 1947. (Unpublished manuscript, Duke
University, Department of Botany. )

Because of its economic importance and wide range, several yield and
growth studies of well- stocked natural stands of loblolly pine have been made
(2, 79, 85, 125). One of these sampled the entire range of the species and
indicated a maximum mean annual growth rate of 1,300 board-feet per acre
(Int. 1/8-inch) in trees 6.6 inches d.b.h. and larger at 45 years, the age of
culmination of mean annual increment for stands of 120-foot site index ( 125 ).
On 60-foot sites the maximum rate was 318 board-feet per acre per year.
Data from permanent sample plots in the Atlantic Coastal States indicated a
possible current annual growth rate of 1,500 to 2,000 board-feet per acre
(Int. 1/4- inch) in trees 9.6 inches d.b.h. and larger on the very best sites at
age 55. Yields at 60 years in trees 6.6 inches d.b.h. and larger range from
19,000 board-feet per acre (Int. l/8-inch) in well-stocked stands of 60-foot site
index up to 73,000 board-feet per acre in stands of 120-foot site index ( 125 ).

Mean annual cubic-foot growth in trees 1.6 inches d.b.h. and larger
ranges from 76 cubic feet per acre at 35 years (culmination of MAI) on a
60-foot site to 204 cubic feet per acre on a 120-foot site ( 125 ). Cubic-foot
yields at 60 years in well-stocked stands vary from 2,400 cubic feet per acre
on the poorest sites to nearly 12,000 cubic feet per acre on the best sites (79).

Mean annual growth in standard cords in trees 3.6 inches d.b.h. and
larger ranges from 0.88 cord per acre per year at 40 years in well-stocked
stands of 60-foot site index up to 2.37 cords per acre per year at 35 years on
120-foot sites ( 128 ). Yields of well-stocked stands at 60 years range from
46 cords per acre on 60-foot sites to 121 cords per acre on 120-foot sites.

In addition to varying with age and site quality, volume growth is
strongly related to stand density, increasing with density up to a maximum
that is higher on good sites than on poor sites (80). The volume growth of
thinned stands also varies with age, site quality, and residual stocking.
Recent studies by the Southeastern Forest Experiment Station suggest that
the growth of thinned and unthinned stands does not differ greatly after one
thinning when age, site quality, and stocking are equal. Although information
presently available is insufficient to compare yields of managed and unman-
aged stands, stands maintained at their optimum density by thinning through-
out the rotation will undoubtedly produce more wood because most moribund
trees will be salvaged and the residual trees will grow faster.

Reaction to competition . --Loblolly pine is classed as an intolerant
species, of the same degree of tolerance as shortleaf pine and Virginia pine,
less tolerant than the oaks, and more tolerant than slash pine and longleaf
pine (3).

The more tolerant hardwoods readily become established in the under-
story of loblolly pine stands, and on uplands throughout the range of loblolly
pine the progress of plant succession is toward a hardwood, oak-hickory
climax (94) . The succession can be most clearly seen in old-field stands
(fig. 4). Light- seeded and intolerant hardwood species, such as sweetgum,
red maple, yellow-poplar, blackgum, and waxmyrtle are early invaders.
Somewhat later the components of the climax, oaks and hickories, appear.

... ,«e*4SWfe W

W!$*

■<

i..'

*»■>«

OS**;

•-. 1

'■\^fc§

if Mt

Thf r V"; 01d " f i eld StSnd ° f l0bl0ll y Pine in the Kisatchie National Forest Louisian*
The understory of small hardwoods has developed since the stand was established

- 17

They increase in size and number as the pine stand matures (jj, 94) and re-
place pines in the overstory as the stand disintegrates between 100 and 300
years of age. Cutting of the pine stand without provision for reestablishment
hastens the process, which accounts for the increase in hardwood types
throughout the loblolly pine range. Fires during the dormant season have
little effect on the succession because the hardwoods sprout prolifically and
vigorously, and even annual dormant- season fires do not reduce the hard-
wood crown area or number of stems (76). However, repeated fires at inter-
vals of less than 10 years ultimately eliminate loblolly pine (30, 134) . Crown
fires destroy the entire stand, as may hot surface fires during the growing
season ( 17), but pine readily becomes reestablished if a seed supply is avail-
able because the hardwoods are also killed back to the ground (93).

Because it is intolerant of shade, loblolly pine expresses dominance
early, and crowns differentiate rapidly under competition on good sites. In
dense stands on poor sites, expression of dominance and crown differentia-
tion are much slower. The density of undisturbed stands approaches an equi-
librium at a rate that probably varies with site quality (21). Well-stocked
stands ranged from 118.7 square feet of basal area per acre for trees 4 inches
in d.b.h. up to 175.4 square feet for trees 16 inches d.b.h. ( 114 ). In
Arkansas, well-stocked stands tended toward a basal area of 155 square feet
per acre (28).

Annual radial growth of loblolly pine is positively correlated with total
rainfall from January to May and negatively correlated with temperature (33) .
It reaches a maximum early in the growing season ( 149 ), and is directly pro-
portional to crown ratio ( 54 , 71), crown length, and total height. -2/ Volume
growth, however, also depends on the length of the clear stem. In 26- year-
old trees, cubic volume growth of the clear stem was greatest with a crown
length that was 40 percent of total tree height (71) .

Loblolly pine prunes itself readily at younger ages, before branches
develop heartwood. The maximum contribution to main- stem growth is made
by branches in the upper portion of the crown, 15 percent of tree height from
the top (71). Below this point the contribution becomes progressively less,
until branches halfway down the stem contribute nothing.

The increase in diameter growth after release is also directly related
to crown ratio, but trees of large diameter respond less than trees of small
diameter ( 26 , 78) . MacKinney (78) found that trees about 60 feet tall increased
diameter growth more than shorter or taller trees after release. Thus, tall,
slender trees with well-developed crowns, that is, codominants and better
intermediates, respond best to release. Trees long suppressed also grow
much faster in both height and diameter after release but may never attain
the growth rate of trees that were never suppressed (26). Height growth

7/ Dubow, D. A. The relationship between crown and bole length and
their ratios with diameter growth in young loblolly pine plantations. 1953.
(Unpublished Master's thesis, North Carolina State College, School of Forestry.)

after release apparently depends mainly on age at release, while diameter
growth depends on crown size and growing space. The capacity of loblolly
pine to respond to release means that noncommercial removal of competing
hardwoods is usually a profitable investment ( 15 , 112 ).

Mortality in loblolly pine stands is caused mainly by competition (16,
111 ), but fire, wind, lightning, sleet, disease, and insects may cause sub-
stantial losses. Accidental fires may completely destroy stands, but more
commonly reduce growth (_4) and cause stump wounds that permit the en-
trance of decay fungi and insects and result in pitch soaking (50). Trees in
repeatedly burned areas develop greater butt swell than unburned trees (2 7).
Large, dominant trees are more vulnerable to wind damage than smaller
trees ( 122 ), and trees with large cankers caused by the southern fusiform
rust break more readily than sound trees ( 135 ). Although direct losses to
lightning are small, averaging only 2 trees per 100 acres per year (122),
lightning- struck trees often become centers of infestations by the southern
pine beetle ( Dendroctonus frontalis) . Other injuries and drought conditions
also favor this insect and it has killed large volumes of loblolly pine through-
out the range. The engraver beetles ( Ips spp. ) and the black turpentine beetle
( Dendroctonus terebrans ) may also cause serious losses under the same cir-
cumstances (84). Sleet storms bend, break, and uproot many trees and may
severely damage heavily stocked stands ( 82 , 91), particularly those made up
of slender, small- crowned trees. Loblolly pine beyond the sapling stage is
seldom killed by disease, but fungi cause appreciable cull in older stands.
Heart rot ( Fomes pini ), entering through branch stubs, and butt rot ( Poly-
porus schweinitzii) , entering through fire wounds, are the most important
causes of such losses (56).

After heavy partial cutting in older stands of moderate or higher den-
sity, many residual trees die from causes directly related to logging and
exposure. Intermediate and suppressed trees may succumb to the drastic
change in environment ( 22 , 74). Isolated dominants and codominants, as in
seed- tree stands, die at the rate of about 1 percent of the number of trees
per year, mainly from wind and lightning ( 32 , 74 , 122 ). Logging injuries and
bark-beetle attack are important causes of death in the first few years after
cutting; puddling of heavy, wet soils and attendant root damage have also
caused substantial losses (81). Ice damage to residual trees is negatively
correlated with live- crown ratio, small- crowned spindling saplings being
most vulnerable (92).

19 -

SPECIAL FEATURES

In common with other hard pines, loblolly pine is highly resinous, al-
though less so than slash pine and longleaf pine. The constitution of the
oleoresin of loblolly pine is as follows (90):

Density 0.8570 22

Index of refraction 1.4675 2 ^-^

Specific rotation, degrees + 20.2

Turpentine yield, percent 19

Turpentine composition, percent 85 d-alpha-pinene

12 1-beta-pinene

The specific gravity of green loblolly pine wood averages 0.47 and
increases from the pith outward. The trend is mainly due to age of the tree
at the time the annual ring is formed and partly due to decreasing width of
rings ( 147 ). Specific gravity is greatest near the base of the tree and de-
creases with height; and it is greater in small- crowned than in large- crowned
trees (97). It also increases as the percentage of summerwood increases.

Tracheid length varies greatly from tree to tree, suggesting that it is
strongly dependent on hereditary factors as well as on environmental con-
ditions (6). Tracheid length averages 4.3 millimeters and ranges from 1.5
up to 7.0 millimeters (14). It increases sharply from the pith outward during
the first 10 years and at a slower rate beyond that point; it also increases
from the base of the tree upwards to middle height and decreases above that
level (6).

The angle made by the fibrils (strands of cellulose that make up the
tracheids) with the main axis of the tracheid is related to longitudinal stability
of lumber and tearing strength of both sulfite and sulfate pulp made from the
wood (98). Large fibril angles are associated with much shrinkage along the
grain and lesser tearing strength of the pulp. Fibril angles in loblolly pine
vary from 2 to 51 degrees, decrease from the pith outward and from the base
of the tree upwards, and are smaller in narrower annual rings. Closely
spaced trees with small crowns have smaller fibril angles than widely spaced,
large- crowned trees.

RACES AND HYBRIDS

Distinct races of loblolly pine have not been identified and described,
but definite variations in survival, growth rate, disease resistance, drought
hardiness, and cold hardiness associated with seed source have been observed.
In tests at several locations in the Southern and Central States, seedlings from
north Alabama seed had a higher survival rate at 2 years than seedlings from
Maryland and Virginia seed, while no seedlings from North Carolina and
South Carolina survived (4_1). In other widely scattered tests in the South,
seed from North Carolina and South Carolina has given better results (130).

- 20

Seedlings from seed of six different sources planted in southern Illinois
showed a significantly different rate of height growth in the first year for
each seed source (88). In another study, Maryland seedlings planted at a
number of places throughout the south grew less in height than those from
other locations, but had exceptionally well- developed fibrous roots ( 130 ).

Near Bogalusa, Louisiana, trees from a local seed source were taller,
larger in d.b.h. , and greater in cubic-foot volume per acre at 22 years than
trees from Texas, Georgia, and Arkansas seed sources ( 129 ). In South Africa,
loblolly pine trees from southern seed sources in the United States were taller
at 9 years than those from northern sources, except that seedlings from
Onslow County, North Carolina, were taller for their latitude, and seedlings
from the Kisatchie National Forest in Louisiana and from the Crossett
Experimental Forest in Arkansas were shorter ( 108 ). At Athens, Georgia,
and Jasper, Texas, the variation in height growth with latitude of seed source
was much less pronounced than in South Africa, but the good performance of
the North Carolina strain and the poor behavior of the Louisiana and Arkansas
strains showed up again ( 129) .

Eastern strains of loblolly have shown a higher susceptibility to fusi-
form rust infection than western strains. In the Bogalusa plantings, 37 per-
cent of Georgia trees were infected, while infection of other strains ranged
from 4 to 6 percent. In the Jasper and Athens plantings, eastern strains had
a much higher incidence of rust than western strains, but northeastern strains,
from Virginia and Maryland, had very few infections in either locality ( 129) .

Cold resistance also varies with seed source. Seedlings of Virginia,
Maryland, Tennessee, and Arkansas strains in nursery beds in southern
Illinois were not damaged by subfreezing temperatures, but North Carolina
seedlings sustained moderate damage, and South Carolina and Mississippi
seedlings sustained moderate to severe damage (89). In Maryland, seed-
lings from local seed were not injured by cold, but those from more southerly
sources were damaged, the southern- most strain- -from Louisiana- -being
conspicuously injured ( 130 ).

Because of its well-known adaptability to a wide range of environmental
conditions, loblolly pine has been planted in many places outside its range. It
has been successfully grown in Australia, New Zealand, South Africa, and
in the coastal region of Uruguay; in the United States it has been grown at
Placerville, California, and in parts of Tennessee, southern Illinois, southern
Indiana, western Kentucky, and southern New Jersey. In Pennsylvania and
Massachusetts, seedlings are winter-killed; in Ohio and southern Indiana,
needles commonly show cold injury (96). Cold also injures loblolly pine in
the Ozarks ( 110 ) .

In the "Lost Pines" area and at the western edge of its range in east
Texas, where summer rainfall is often deficient, loblolly pine is apparently
more drought hardy than it is farther east. In a test in east Texas, seed-
lings from that locality had consistently better survival than seedlings from
Louisiana, North Carolina, and Florida ( 154) . No differences in growth among
the surviving seedlings were observed, however.

- 21

Variations in the behavior of individual trees have also been traced to
hereditary factors. In South Carolina, seedlings from different mother trees
differed significantly in height growth and survival (87).

One natural hybrid involving loblolly pine has been identified and named.
This is the hybrid known as Sonderegger pine (Pinus x sondereggeri) . It is
common in Louisiana, and perhaps elsewhere, in longleaf stands near a source
of loblolly pine pollen ( 25 , 43 ) . The seed apparently comes from longleaf pine
trees; hence loblolly pine is probably the male parent. Many trees with char-
acteristics intermediate between those of shortleaf and loblolly pine, which
may be hybrids, have been found in east Texas ( 153) and may occur wherever
these two species grow in mixture. Loblolly pine flowers before shortleaf pine
but early conelets of shortleaf pine may become receptive while loblolly pine
pollen is still being cast; or loblolly pine flowering may occasionally be re-
tarded by cold weather so that loblolly pine conelets might still be receptive
when shortleaf pine starts pollinating. Where loblolly and pond pine are
closely associated, pines with intermediate characteristics between these
two species are common.

Interspecific hybrids of loblolly pine are not difficult to obtain (4_3) and
a number of successful hybrids have been produced by controlled pollination.
Some successful hybrids that have been reported are as follows (18, 19, 38,
107, 133):

Seed parent Pollen parent

Shortleaf Loblolly

Slash

Pitch

Longleaf "

Loblolly Pitch

Shortleaf x loblolly Loblolly

Loblolly Shortleaf

Slash

Shortleaf x loblolly Loblolly x slash

Loblolly x slash Slash

Loblolly Sonderegger

" Shortleaf x loblolly

Shortleaf Shortleaf x loblolly

Shortleaf x loblolly Loblolly x slash

Shortleaf x slash Sonderegger

Longleaf Sonderegger

Seedlings from a cross between loblolly pine and South Florida slash
pine ( Pinus elliottii var. densa) are growing at Hamilton, Georgia, and at
the Southern Institute of Forest Genetics near Gulfport, Mississippi. -2/
Seedlings of pond x loblolly pine are growing at the Westvaco Experimental
Forest, near Georgetown, South Carolina (37).

&J Dorman, K. W. Official correspondence, Tidewater Forest
Research Center, Franklin, Virginia. April 27, 1956.

- 22 -

LITERATURE CITED

(1) American Forestry Association

1956. THESE ARE THE CHAMPS. Part II. Amer. Forests 62(4): 33-40.

(2) Ashe, W. W.

1915. LOBLOLLY OR NORTH CAROLINA PINE. N. C. Geol. and Econ. Survey

Bui. 24, 176 pp., illus.

(3) Baker, F. S.

1949. A REVISED TOLERANCE TABLE. Jour. Forestry 47: 179-181.

(4) Barrett, L. I.

1928. FIRE DAMAGE TO MATURE LOBLOLLY PINE. Naval Stores Rev. 38(18): 11.

(5) and Downs, A. A.

1943. HARDWOOD INVASION IN PINE FORESTS OF THE PIEDMONT PLATEAU.

Jour. Agr. Res. 67: 111-127.

(6) Bethel, J. S.

1941. THE EFFECT OF POSITION WITHIN THE BOLE UPON FIBER LENGTH OF

LOBLOLLY PINE. Jour. Forestry 39: 30-33.

(7) Bormann, F. H.
1953. FACTORS DETERMINING THE ROLE OF LOBLOLLY PINE AND SWEET-
GUM IN EARLY OLD- FIELD SUCCESSION IN THE PIEDMONT OF NORTH
CAROLINA. Ecol. Monog. 23: 339-358.

1956. ECOLOGICAL IMPLICATION OF CHANGES IN THE PHOTOSYNTHETIC

RESPONSE OF PINUS TAEDA SEEDLINGS DURING ONTOGENY. Ecology
37: 70-75.

(9) Boyce, J. S., Jr.

1951. LOPHODERMIUM PINASTRI AND NEEDLE BROWNING OF SOUTHERN
PINES. Jour. Forestry 49: 20-24.

(10)

1952. SCIRRHIA ACICOLA, A CAUSE OF LOBLOLLY PINE NEEDLE BROWNING.
Assoc. South. Agr. Workers Proc. 49: 134.

(11)

1954. HYPODERMA NEEDLE BLIGHT OF SOUTHERN PINE. Jour. Forestry 52:

496-498.

(12) Brender, E. V., and Barber, J. C.

1956. INFLUENCE OF LOBLOLLY PINE OVERWOOD ON ADVANCE

REPRODUCTION. U. S. Forest Serv. Southeast. Forest Expt. Sta.
Paper 62, 12 pp., illus. (Processed.)

(13) and Nelson, T. C.

1954. BEHAVIOR AND CONTROL OF UNDERSTORY HARDWOODS AFTER CLEAR

CUTTING A PIEDMONT PINE STAND. U. S. Forest Serv. Southeast. Forest
Expt. Sta. Paper 44, 17 pp., illus. (Processed.)

(14) Brown, H. P., and Panshin, A.J.

1940. COMMERCIAL TIMBERS OF THE UNITED STATES. 554 pp., illus.

New York and London.

(15) Bull, H.

1945. INCREASING THE GROWTH OF LOBLOLLY PINE BY GIRDLING LARGE

HARDWOODS. Jour. Forestry 43: 449, 450.

(16)

1950. CORD MORTALITY IN UNTHINNED STANDS. U. S. Forest Serv. South.

Forest Expt. Sta. South. Forestry Notes 70. (Processed.)

(17) Byram, G. M.

1948. VEGETATION TEMPERATURE AND FIRE DAMAGE IN SOUTHERN PINES.

U. S. Forest Serv. Fire Control Notes 9(4): 34-36.

(18) California Forest and Range Experiment Station

1948. TIMBER PINE HYBRIDIZATION. Ann. Rpt. 1947: 13, 14.

(19)

1952. NEW HYBRIDS RESULT FROM EARLIER ATTEMPTS. Ann. Rpt. 1952: 13, 14.

(20) Cech, F.

1955. VEGETATIVE PROPAGATION OF LOBLOLLY PINE. Texas Forest Serv.

Cir. 51, 13 pp., illus.

(21) Chaiken, L. E.

1939. THE APPROACH OF LOBLOLLY AND VIRGINIA PINE STANDS TOWARD

NORMAL STOCKING. Jour. Forestry 37: 866-871.

(22)

1941. GROWTH AND MORTALITY DURING 10 YEARS FOLLOWING PARTIAL

CUTTINGS IN LOBLOLLY PINE. Jour. Forestry 39: 324-329.

(23) and LeGrande, W. P., Jr.

1949. WHEN TO BURN FOR SEEDBED PREPARATION. Forest Farmer 8(11): 4.

(24) Chandler, R. F., Schoen, P. W., and Anderson, D. A.

1943. RELATION BETWEEN SOIL TYPES AND THE GROWTH OF LOBLOLLY

PINE AND SHORTLEAF PINE IN EAST TEXAS. Jour. Forestry 41: 505, 506.

(25) Chapman, H. H.

1922. A NEW HYBRID PINE ( PINUS PALUSTRIS X PINUS TAEDA ). Jour. Forestry

20: 729-735.

(26)

1923. THE RECOVERY AND GROWTH OF LOBLOLLY PINE AFTER SUPPRESSION.

Jour. Forestry 21: 709-711.

(27)

(28)

(29)

(30)

1942. EFFECT OF ANNUAL SPRING FIRES ON STUMP TAPER OF LOBLOLLY

PINE. Jour. Forestry 40: 962, 963.

1942. MANAGEMENT OF LOBLOLLY PINE IN THE PINE-HARDWOOD REGION

IN ARKANSAS AND IN LOUISIANA WEST OF THE MISSISSIPPI RIVER. Yale
Univ., School Forestry Bui. 49, 150 pp., illus.

1945. THE EFFECT OF OVERHEAD SHADE ON THE SURVIVAL OF LOBLOLLY

PINE SEEDLINGS. Ecology 26: 274-282.

1948. HOW TO GROW LOBLOLLY PINE INSTEAD OF INFERIOR HARDWOODS.

Soc. Amer. Foresters Proc. 1947: 347-353.

(31) Chase, S. B. , and Galle, F. C.

1954. PINE GRAFTING. Tenn. Valley Authority Tech. Note 18.

(32) Clark, S. F., and Hebb, E. A.

1951. MORTALITY FOLLOWING HARVEST CUTTING. U. S. Forest Serv. South.

Forest Expt. Sta. South. Forestry Notes 74. (Processed.)

(33) Coile, T. S.

1936. THE EFFECT OF RAINFALL AND TEMPERATURE ON THE ANNUAL

RADIAL GROWTH OF PINE IN THE SOUTHERN UNITED STATES. Ecol.
Monog. 6: 533-562.

(34)

1940. SOIL CHANGES ASSOCIATED WITH LOBLOLLY PINE SUCCESSION ON

ABANDONED AGRICULTURAL LAND OF THE PIEDMONT PLATEAU.
Duke Univ. Forestry Bui. 5, 85 pp., illus.

(35)

1948. RELATION OF SOIL CHARACTERISTICS TO SITE INDEX OF LOBLOLLY

AND SHORTLEAF PINES IN THE LOWER PIEDMONT OF NORTH CAROLINA.
Duke Univ. Forestry Bui. 13, 78 pp., illus.

(36) and Schumacher, F. X.

1953. RELATION OF SOIL PROPERTIES TO SITE INDEX OF LOBLOLLY AND

SHORTLEAF PINES IN THE PIEDMONT REGION OF THE CAROLINAS,
GEORGIA, AND ALABAMA. Jour. Forestry 51: 739-744.

(37) Committee on Southern Forest Tree Improvement

1956. WESTVACO COLLECTS OVER 5,000 POUNDS OF SEED. Newsletter 5(1): 5.

(38)

1956. EXTENSIVE HYBRIDIZATION IS CARRIED OUT AT THE SOUTHERN

STATION. Newsletter 5(1): 7.

(39) Cooper, W. E.

1942. FOREST SITE DETERMINATION BY SOIL AND EROSION CLASSIFICATION.

Jour. Forestry 40: 709-712.

(40) Craighead, F. C.

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1957. INDICES TO POTENTIAL CONE PRODUCTION OF LOBLOLLY PINE. Jour.

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1937. THE PHYSICAL BASIS OF MYCOTROPHY IN PINUS. Black Rock Forest
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1957. SOME FURTHER EVIDENCE OF COMPETITION BETWEEN LOBLOLLY

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1951. SURVEY GIVES NEW INFORMATION ON INSECT DAMAGE TO LOBLOLLY

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1936. EFFECT OF VARIATION IN LENGTH OF DAY ON GROWTH AND DORMANCY

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1942. SPECIES DIFFERENCES WITH RESPECT TO WATER ABSORPTION AT LOW

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1943. AMOUNT AND DURATION OF GROWTH OF VARIOUS SPECIES OF TREE

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1952. SURVIVAL OF PINE AND HARDWOOD SEEDLINGS IN FOREST AND OPEN.
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1954. REPRODUCING PINE STANDS ON THE EASTERN SHORE OF MARYLAND.

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1957. GROWTH AND MORTALITY OF RESIDUAL LOBLOLLY PINES AFTER A

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1957. SEEDBED TREATMENT INCREASES DOMINANCE OF NATURAL LOBLOLLY

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1956. GOOD SEED PRODUCTION FROM A YOUNG STAND OF LOBLOLLY PINE.

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1939. VOLUME, YIELD, AND GROWTH OF LOBLOLLY PINE IN THE MID-
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1955. THE RELATION OF GROWTH TO SITE AND RESIDUAL DENSITY IN LOB-
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1950. WET WEATHER LOGGING MAY DAMAGE SEED TREES. Va. Forests 5(5): 6.

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1942. ICE DAMAGE TO SLASH PINE, LONGLEAF PINE, AND LOBLOLLY PINE

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1940. THE NATURAL ESTABLISHMENT OF PINE IN ABANDONED FIELDS IN
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1956. FOREST INSECT CONDITIONS IN THE SOUTHEAST. U. S. Forest Serv.
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1942. YIELD OF EVEN- AGED STANDS OF LOBLOLLY PINE IN NORTHERN

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1955. SOME TREATMENT EFFECTS ON LOBLOLLY AND SHORTLEAF PINE

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1942. ONE-PARENT HEREDITY TESTS WITH LOBLOLLY PINE. Jour. Forestry

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1950. EFFECT OF SEED SOURCE ON HEIGHT GROWTH OF PINE SEEDLINGS.

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1951. SOUTHERN PINE FROM DIFFERENT GEOGRAPHIC SOURCES SHOW

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1954. CHEMICAL COMPOSITION OF GUM TURPENTINES OF THE U. S. AND

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1947. ICE DAMAGE TO PINE PLANTATIONS. South. Lumberman 175(2201):

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(92) Nelson, T. C.

1951. ICE DAMAGE HIGH FOR SPINDLY RESIDUAL SAPLINGS. Forest Farmer

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1944. THE COMPARATIVE EFFECT OF SURFACE AND CROWN FIRE ON THE

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1948. PLANT COMMUNITIES. 389 pp. , illus. San Francisco.

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1946. WATER AND LIGHT IN RELATION TO PINE REPRODUCTION. Ecology

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1950. PLANTING LOBLOLLY PINE OUTSIDE ITS NATURAL RANGE. Jour.

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1954. SPECIFIC GRAVITY RELATIVE TO CHARACTERISTICS OF ANNUAL

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1953. PATTERNS OF VARIATION IN FIBRIL ANGLES IN LOBLOLLY PINE. U. S.

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1949. LOBLOLLY PINE SEED TREES: SELECTION, FRUITFULNESS, AND
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1949. THE GERMINATION AND INITIAL ESTABLISHMENT OF LOBLOLLY PINE

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1955. PRESCRIBED BURNING IN LOBLOLLY PINE MANAGEMENT. Fourth Ann.

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1939. EARLY FLOWER PRODUCTION AMONG THE PINES. Jour. Forestry 37:

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1951. INTERSPECIES HYBRIDS IN PINES. Jour. Heredity 42: 75-80.

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1947. THE POTENTIALITIES OF GENETIC RESEARCH IN SOUTH AFRICAN

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1954. RELEASE OF LOBLOLLY PINE BY VARIOUS WEEDING METHODS. U. S.

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1947. EARLY RESULTS OF A LIBERATION CUTTING IN A PINE-HARDWOOD

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1954. FOREST COVER TYPES OF NORTH AMERICA (EXCLUDING MEXICO).

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1949. THINNING EVEN-AGED LOBLOLLY AND SLASH PINE STANDS TO
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1952. THE RED- COCKADED WOODPECKER. Va. Wildlife 13(8): 18, 19.

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1950. A METHOD OF FORECASTING ANNUAL VARIATION IN SEED CROP FOR

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1947. TREES IN THE EDDY ARBORETUM. U. S. Forest Serv. Calif. Forest

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1944. THE BOB-WHITE QUAIL IN EASTERN MARYLAND. Md. Game and Inland

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1952. POLLEN DISPERSION OF SOME FOREST TREES. U. S. Forest Serv.
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1956. EXPERIMENTAL AIR- LAYERING OF SHORTLEAF AND LOBLOLLY PINE.

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